Caliper brakes are extensively used in passenger vehicles, commercial vehicles and racing vehicles. The brake system is relatively straight forward with brake pads being applied on opposite sides of a brake rotor often referred to as a brake disk. Racing brakes are subject to higher operating temperatures and it is desirable to operate these brakes at reduced temperatures to increase the life of the brakes and to make them more effective during each braking operation. Various arrangements for dissipating heat have been used to improve brake performance and extend the effective life of the brake pads and rotors. The brake pads are forced by one or more hydraulic pistons against the brake rotor and removal of the hydraulic pressure allows the brake pads to move to a release position. Although positive retraction of the brake pads due to a bias force is desirable, a cost effective and reliable system has been difficult to achieve.
A positive cost effective and reliable retraction mechanism for moving the brake pads sufficiently to space the brake pads from the brake rotor when the brakes are not applied is desirable. Such an arrangement would reduce heat buildup and increase the life and performance of the brake system.
There have been a number of caliper brake designs that include a separate spring type mechanical arrangement for retracting the brake pads relative to the brake rotor. Although a separate mechanical arrangement can operate satisfactorily, problems occur in more difficult environments associated with an actual road brake and/or conditions on the race track or with respect to manufacturing costs. Furthermore, a number of race restriction rules ban the use of a mechanical spring type retraction system.
In caliper brakes for racing vehicles, one or more pistons force the brake pads against the caliper and the pistons include a specialized seal to isolate and maintain the hydraulic fluid effectively captured behind the piston. The problem of sealing each piston becomes more difficult as the operating temperature of the caliper brake increases. In most applications an ethylene propylene diene monomer (EPDM) seal is used as an effective seal between the piston and the cylinder. For demanding applications (high temperature racing) a fluoral elastomer KALREZ™ may be used. One commercially available material is sold with the KALREZ trademark. When the temperature of the brake becomes too high, some seal materials lose elasticity and permanently distort, resulting in brake fluid leaks and failure. By retracting sufficiently the lower cost EPDM seal is often sufficient.
It has been found that a retraction arrangement for the brake caliper is preferably separated from the seal and not exposed to brake fluid. Preferably the retraction mechanism has a dry interface between the cylinder and the piston, and a resilient biasing member is provided in a specific space and compressed with actuation of the brake pads. Preferably the retraction mechanism can be mechanically adjusted to vary the amount of positive retraction.